It is well known in the art of transmission lines for electromagnetic signals in antennas to use feed systems implementing Orthogonal Mode Junction (OMJ) with waveguide networks for both Tx (transmit) and Rx (receive) signal paths. Such implementation, especially for on-board spacecraft applications, typically fulfils operation requirements such as:                combined Tx and Rx functionality;        dual circular or linear polarization functionality;        high Tx-Rx signal isolation;        low signal insertion loss;        excellent signal XPD (Cross Polar Discrimination) and axial ratio performance;        good thermal dissipation capability; and        low PIM (Passive Inter-Modulation) products.        
These requirements are also typically tied with the smallest possible overall volume and the lowest possible mass of the antenna feed systems.
However, the typical relatively large overall volume and mass achieved with such antenna feed systems implementations, including an OMJ with waveguide network for both Tx and Rx signals paths, preclude their use in many applications, where the volume and the mass should still be reduced by at least a factor of two (2).
Although other designs such as TEM-line networks, utilizing a simple coupler 100 shown in FIGS. 1-4, including an electrically conductive center or inner conductor 102 (with a branch-line coupler centrally located 103) supported by dielectric supports 104 inside a channeled electrically conductive outer conductor, typically made out of a channeled base part 106 and a generally flat top cover part 108, are typically smaller and lighter, they have the drawbacks of not being capable of achieving other requirements. Effectively, the electrically isolating dielectric supports of the center conductor limit the signal power handling because of heat generation due to signal losses within the supports that need to be dissipated (in vacuum environment for space applications). This in turn generally increases the overall insertion loss of the antenna system, and therefore decreases the performance of the antenna.
Accordingly, there is a need for an improved compact and lightweight TEM-line network for antenna system, and associated dual-band antenna feed system.